Williams said: “I just can’t serve. I mean, my serve hasn’t been good yet. I can’t say this whole tournament, because my tournament didn’t last long, but just in general.

“I hate to be off during a grand slam, but it happens. It’s not the end of the world.”

Muguruza, ranked 35th in the world, admitted she was feeling the pressure with the end of the match in sight.

She said: “There was a moment in the last games of the match, I was like ‘oh my god, I’m winning the set’. I was nervous, but I said ‘be calm, she’s nervous also. I have the opportunity, so I have to continue like this to win’.”

Williams’ sister Venus was beaten in three sets by Slovakia’s Anna Schmiedlova, but upsets were scarce in the men’s draw as top 10 seeds Novak Djokovic, Roger Federer and Tomas Berdych all reached round three.

British No1 Andy Murray takes on world No66 Marinko Matosevic of Australia in his second round match today.

Murray beat the 28-year-old, who plays in the second round of a grand slam for the first time in his career, in their only previous meeting at Queen’s Club last year, shortly before lifting the Wimbledon title.